Abstract Ischemic heart disease remains as the single largest leading causes of death in the U.S.A. accounting for more than 1 in 3 deaths per annum. Acute ischemic injury and chronic cardiomyopathy lead to permanent loss of cardiac tissue and ultimately heart failure. Developing novel therapeutic approaches that can directly target the causes of cardiomyocyte death during Ischemia/Reperfusion (IR) injury will have broad translational potential. Our recent findings suggest that MG53, a novel muscle-specific member of the TRIM family of proteins (TRIM72), is essential for repair of muscle damage, and also provide a therapeutic target for treatment of cardiovascular diseases. This application focuses on testing our hypothesis that "MG53 is an essential molecule for myocardial repair following ischemia-reperfusion injury, and extracellular recombinant MG53 may promote myocardial repair and prevent ischemic heart disease". In specific aim 1, we will examine the mechanism underlying MG53-mediated myocardial repair under conditions of oxidative-stress, ischemia or acute injury with isolated cardiomyocytes from neonatal mice. Aim 2 of this proposal will establish the efficacy of recombinant MG53 in protection against IR injury to the heart muscle using the wild type and mg53-/- animal models. Specifically, we will determine if the application of MG53 protein prior to or after reperfusion can prevent or attenuate ischemia-reperfusion induced myocardial injury. Fulfillment of the proposed experiments may provide the essential proof-of-principle studies on the feasibility of targeting MG53 in treatment of ischemic heart disease. PUBLIC HEALTH RELEVANCE: Project Narrative Ischemic heart disease is the most common cause of death in most Western countries. Developing novel therapeutic approaches that can directly target the causes of cardiomyocyte death during Ischemia/reperfusion (IR) injury will have broad translational potential. One pathway with great potential as a therapeutic target in regenerative medicine is the process by which individual cells repair their plasma membrane following injury. We recently found that MG53 is a novel, muscle-specific member of the TRIM family of proteins (TRIM72), which contributes to the dynamic membrane repair process in skeletal muscle (1-3). However, the role of MG53 in myocardial protection remains unknown. In this application, we will conduct experiments to investigate the impacts of MG53 in myocardial repair following Ischemia/reperfusion injury. Initially, we will use both wild type and MG53 knockout mice models to investigate the mechanism underlying MG53-mediated repair of membrane damage to cardiomyocytes under conditions of oxidative-stress, ischemia or acute injury. We will also assess the efficacy of recombinant MG53 protein in protection against IR injury to the heart muscle using comprehensive evaluation of myocardial performance, including echocardiography, immunohistochemistry and confocal microscopy with the wild type and MG53 knockout mice. The results will provide novel insights into proof-of-principle studies to develop effective protein-based therapies for cardiac repair in patients with cardiovascular diseases.